Control apparatus



A. B. NEWTON 2,303,654

CONTROL APPARATUS Dec. 1, 1942.

Filed July 12, 1940 3 2 g 5 P0 0 E 2: 2'1" Q DETECTOR AND AMPLIFIER INVENTOR Alwin- 1B. Newtom ATTORNEY Patented Dec. 1, 1942 UNITED STATES PATENT OFEQE Minneapolis-Honeywell Regulator Company,

Minneapolis, Minn., a corporation oi Delaware Application July 12, 1940, Serial No. 345,251

12 Claims.

This invention relates to control apparatus wherein condition responsive devices are used to modulate a high frequency current.

An object of this invention is to provide an improved control system including a frequency responsive control device and means to vary the frequency of the current supplied to the control device in accordance with the magnitude of a condition.

A further object is to provide an improved control system including a control device selectively operable in either of two directions, and means responsive to the direction of departure of a condition from a predetermined value to determine the direction of operation oi said control device.

A further object is to provide an improved control system including a control device variable in speed and selectively operable in either of two directions, and means responsive to the direction of departure of a condition from a predetermined value to determine the direction of operation of said control device, and responsive to the magnitude of such departure to regulate the speed of said control device.

A further object of the invention is to provide an improved control system of the type described which shall be extremely sensitive to small changes in the controlling condition.

I accomplish the objects set forth by operating the control device of my system with a split phase motor which is variable in speed in accordance with the frequency of the current supplied to its terminals, and variable in direction of rotation in accordance with the phase relations of said current. This motor is supplied with energy obtained by heterodyning the outputs of two oscillators. One oscillator is set to produce a standard frequency, while the frequency of the other oscillator is varied in accordance with the magnitude of the controlling condition. The beat frequency, and therefore the motor speed is determined by the magnitude of the departure of the controlling condition from a datum determined by the standard frequency.

It is a well known fact that the beat wave produced by combining a wave of certain standand frequency with another wave of frequency, for example, 200 cycles lower than the standard, is displaced in phase 180 from the beat wave produced by combining a wave of the same standard frequency with another 200 cycles higher than the standard. This phenomenon is utilized in my invention to determine the direction of rotation of the motor which drives the control device.

Other objects of the invention will be apparent from the accompanying specification, claims, and drawing, which is a wiring diagram of a control system embodying my invention.

In the drawing, l0 represents a valve operated by a rack II and cooperating pinion l2 which is driven by a motor generally indicated at 53 through a reduction gear shown diagrammatically at H. Motor i3 is of the split phase type having field windings l6 and I! and a rotor it. Each of the windings l6 and ll is supplied with current from a separate source. The speed of the motor depends upon the frequency of the current supplied to the windings and the direction of rotation depends upon the phase relations between the currents flowing in the two windings. That is to say, if the current in winding l6 leads the current in winding H the motor will rotate in one direction, for instance clockwise, while it the current for winding ll leads the current in winding I6 the motor will rotate in the opposite direction, or counter-clockwise.

The energization of winding I6 is controlled in accordance with the current flow in a secondary winding IQ of an air core transformer generally indicated at 20. The air core transformer 2'0 is also provided with two primary windings 2i and 22. is connected to the input terminals of a detector and amplifier circuit schematically shown at 23.

The output terminals of the detector and ampli fier 23 are connected through conductors 24 and 25 to the winding IS.

The energizationof winding I! is similarly controlled in accordance with the current flow in a secondary winding 26 of an air core transformer generally indicated at 2i. The transformer 21 is also provided with two primary windings 28 and 29. The secondary winding 26% is connected to the input terminals of a detector and amplifier schematically indicated at 30. The output terminals of the detector and amplifier 30 are connected through conductors 3i and 32 to the motor winding 41.

An oscillator circuit indicated generally at serves to supply high frequency current to the primary windings 22 and 29 of transformers 20 and 21, respectively. A second oscillator circuit generally indicated at 34 supplies current to the primary windings 2| and 28 of transformers 2d and 21, respectively.

The oscillator circuit 33 comprises an electric discharge device 35 of any suitable type, being The secondary winding it shown as a triode comprising an anode 36, a control electrode 31, a cathode 38, and a heater filament 39. The input circuit of the triode 35 may be traced from cathode 38 through a conductor 49, a variable condenser 4| in parallel with an inductance 4.: and a coupling condenser 43 to the control electrode 31. The output circuit of the triode 35 may be traced from anode 36 through an inductance 44, a conductor 45, primary winding 22 of transformer 29, a conductor 46, primary winding 29 of transformer 21, a conductor 41, and a voltage dividing resistor 48 to cathode 38. The inductances 44 and 42 are coupled in a well known manner so as to provide a feed back from the output circuit to the input circuit. The heater filament 39 is connected between the cathode 38 and a suitable tap 49 on the voltage dividing resistor 48. The frequency of this scillator circuit may be adjusted to any desired value by adjusting the variable condenser 4|. It will be understood by those skilled in the art that this is a conventional oscillator circuit and that any convenient oscillator circuit may be used in my control system without departing from the spirit of the invention.

The oscillator circuit 34 is in general similar to the oscillator circuit 33 except that the variable condenser 4| is replaced by three variable condensers SI, 62, and 63 which are connected in series. The variable condenser 6| has a set of stationary plates 64 and a set of movable plates 65 which are biased by a spring 93 so as to move toward the stationary plates 64. A humidity re sponsive element 61 opposes the biasing spring 66. The element 61 is preferably of the type which decreases in tension upon an increase in humidity. It will therefore be seen that an increase in humidity causes the plates 65 to move closer to the plates 84 thereby increasing the capacitance of condenser 6|. Variable condenser 62 is provided with a stationary set of plates 68 and a set of movable plates 69, the latter being positioned relative to the stationary plates by a temperature responsive device 19 shown in the drawing as a bimetallic spiral. This bimetallic spiral is so constructed that an increase in temperature causes the movable plates I59 to move toward the stationary plates 68. It will therefore be apparent that an increase in temperature causes an increase in the capacitance of the condenser 92. Condenser 63 is provided with a set of stationary plates 1| and a set of movable plates 12. The movable plates 12 are eccentrically mounted on a shaft 13 which is connected to the reduction gear mechanism I4.

The oscillator circuit 34 comprises an electric discharge device 15 of any desired type being shown as a triode having an anode 16, a control electrode 11, a cathode 18, and a heater filament 19. The input circuit of triode 15 may be traced from cathode 18 through a conductor 89, an inductance 8|, and a coupling condenser 82 to the control electrode 11. .The condensers SI, 62, and 63 are also connected in the input circuit through a connection which may be traced from the lower end of the inductance 8| through a conductor 83, condenser 6|, a conductor 84, temperature responsive element 19, condenser 62, a conductor 85, condenser 63, and a conductor 86 to the upper end of inductance 8|. The output circuit of triode 15 may be traced from anode 16 through an inductance 81, a conductor 88, primary winding 2| of transformer 29, a conductor 89, and a voltage dividing resistor 99 to cathode 18. The heater filament 19 is connected between the cathode ,high voltage secondary II4. the secondary 4 are connected to the input 19 and a suitable tap I92 of the voltage dividing resistor 99. The inductance 81 is associated with the inductance 8| so as toprovide the necessary feed back from the output circuit to the input circuit of-triode 15. An input winding 9| of a phase shifting bridge generally indicated at 92 is connected in parallel with the primary winding 2| of transformer 29. This connection may be traced from the upper end of transformer primary 2| through a conductor 92, input winding 9|, conductors 93 and 94 to the righthand terminal of resistor 99. The phase shifting bridge 92 is of a conventional type having a secondary winding 95 associated with the input winding 9|. Connected in series across the terminals of the winding 98 are a resistor 96 and an impedance 91. The output terminals of the phase shifting bridge 92, comprising a tap 99 located centrally of the secondary winding 95 and common terminal 99 of the resistor 98 and impedance 91, are connected through conductors I99 and IN, respectively, to the terminals of primary winding 29 of transformer 21.

The control system is supplied with energy from lines 9 and III through a transformer II2 comprising a line voltage primary H3 and a The terminals of terminals of a rectifier schematically indicated at H5. The output terminals of rectifier II! are connected through conductors H9 and H1 to a voltage dividing resistor II9. Resistor H8 is provided with terminals H9 and I29 and intermediate taps I2I, I22, and I23. The oscillator circuit 34 is supplied with energy from the resistor I I8 through a circuit which may be traced from terminal II9 through conductors I24 and I25, resistor 99, conductors 94, I29, and I21 to tap I2I.' A filtering condenser I29 is connected between conductors I2I and I24 to prevent the flow of high frequency current in the resistor H8. The oscillator circuit 33 is supplied with energy through a similar circuit which may be traced from tap I2I through conductors I21 and I29, resistor 49, conductors I39, I3I, and I32 to tap I22. A filtering condenser I49 is connected between conductors I21 and I32 in order to prevent the fiow of high frequency current from the oscillator circuit through resistor H8.

The detector and amplifier 39 is supplied with power through a circuit which may be traced from tap I22 to conductors I32, I3I, and Ill, detector and amplifier 39, conductors I42, I43, and I44 to tap I23. A filtering condenser I45 is connected between conductors I32 and I44. Detector and amplifier 23 is supplied with power through a circuit which may be traced from tap I23 through conductors I44, I43, and I49, detector and amplifier 23, conductors I41 and I48 to terminal I29. A filtering condenser I49 is connected between conductors I44 and I48.

Operation In describing the operation of my system, it will first be considered, for the sake of simpliflcation, as though the humidity-responsive condenser GI were removed, and the only conditionresponsive device in the system was the temperature-responsive condenser 62.

The condenser 62 and its bimetallic operating member 19 are located in a room or space whose temperature it was desired to control by means of my system. The valve I9 controls the supply of heating fluid, for example, steam to the room.

When placing my system in operation, the osfrequency to the motor winding l6. time, in the transformer 21 currents of the same manually until the room temperature reaches the desired value. At that time, the oscillator circuit 34 will have a certain frequency, dependent upon the capacitance of condensers Blend 63, as determined by the room temperature and the condenser position, respectively. This is "taken as the standard frequency, and the frequency of oscillator circuit 33 is varied by means of condenser 4 1, until it is operating at the standard frequency, This condition may be readily determined, since when both oscillators are ,operating at the same frequency, motor l3 will not be rotated. When this condition has been obtained, the valve l and condenser 63 are operativelyconnected to the motor i 3, and the system is then in operation.

The oscillator circuits 33 and 34 operate at relatively high frequencies, for example, several kilocycles, while the motor I3 is of conventional type, andis suitably operated only by currents having a frequency of, for example, less than 100 cycles. The outputs of oscillators 33 and 34 are combined in the transformers 20 and 21, so that the secondary windings l9 and 26 of these transformers carry high frequency current. If the frequencies of oscillators 33 and 34 are different, the secondary windings l9 and 26 also carry a beat frequency current having a frequency equal to the difference between the primary frequencies.

The detector and amplifier circuits 23 and 30 are designed to prevent the passage of high frequency current from the transformers 20 and 21 to the motor windings l6 and I! while permitting the passage of low frequency current such as would be suitable to operate the motor.

If the frequencies of oscillator circuits 33 and 34 are the same no beat frequency appears in the secondary windings I9 and 26. Therefore no current is produced in the output circuits of the amplifiers 23 and 30 and. the motor I3 is not energized. If the temperature of the space being controlled changes, however, from its desired value, a corresponding change takes place in the capacitance of condenser 62, which causes a change in the frequency of oscillator 34. In the transformer 20 there will then be a difference in the frequencies of the currents supplied to the primary windings. As a result, the secondary winding 19 will carry currents of both primary frequencies and in addition a current of beat frequency, which is equal to the difference between the primary frequencies. The detector and amplifier 23 will pass only the current of the beat At the same two primary frequencies will be applied to the primary windings 26 and 28. Because of the action of the phase shifting bridge 92, however,

the current supplied to winding 28 will differ in phase approximately 90 from the current supplied to the primary winding 2! of transformer 20. There will be produced in the secondary winding 26 high frequency currents of both the applied frequencies and another current of their beat frequency. This beat frequency current will be of the same frequency as the beat frequency current in secondary winding 69 of transformer 20. Because of the difference in phase of the currents in primaries 2| and 28, however, the beat frequency current in winding 26 will differ in phase by approximately from that in winding IS. The beat frequency current in Winding 26 will be amplified in the amplifier 30 and applied to the terminals of motor winding IT. The motor l3 will then have supplied to its windings currents of equal frequency but differing in phase by 90.

It will be understood by those skilled in the art that these are the proper conditions to produce rotation of a split phase motor of the type described, and that the speed of rotation of the motor l3 will be dependent on the frequency of the current supplied to it. Therefore, it will be seen that the motor I3 will be driven at a speed corresponding to the magnitude of the departure of the effective temperature of the room or space being controlled from its desired value. duce a rapid rotation of the motor 13 whereas a small change will produce a smaller rotation. Motor 13, in addition to operating the valve In to vary the supply of heating fluid to the room or space under control operates, through the shaft 13, the variable condenser 63. When a change occurs in the temperature of the room under control a rotation of the motor [3 takes place as described above. The direction of rotation of this motor is such as to vary the capacitance of condenser H in the opposite sense to that in which the capacitance of condenser 62 was varied by the temperature change. It will be seen therefore that a reduction in temperature of the space under control will cause rotation of the motor l3 until the frequency of the oscillator circuit 34 is restored to its original value by the balancing action of the variable condenser 63. During this rotation the valve i0 will be opened by a certain definite amount depending upon the magnitude of the variation in temperature. For any given temperature of the space under control therefore this system provides an accurate positioning of the valve 1 0.

The change in frequency produced in the oscil-v lator circuit 34 by a decrease in temperature of the room will be opposite in sense to that pro duced by an increase in temperature of the room. For example, if an increase in temperature of 2 causes an increase in frequency of 25 cycles, a decrease in temperature of 2 will cause a decrease in frequency of 25 cycles.

When a current of variable frequency is com-' bined with a current of constant frequency to produce a beat frequency, a difference in phase of will be observed between the beat frequency produced when the variable frequency is higher than the standard frequency, and the beat frequency produced when the variable frequency is lower than the standard. As a result of this phenomenon the current in the winding l6 will lead the current in winding l! by about 90. When the condition to which the condenser 32 is responsive is displaced in one direction from its established datum while the current in the winding ll will lead that in the winding iii when the condi tion is displaced in the opposite direction. Consequently the direction of rotation of the motor 93 will be determined by the sense of change of the condition to which condenser 62 is responsive. it

A large change in temperature Will pI'O- directly to the line 86.

will be seen therefore that this system will operate the variable condenser 62 in the proper sense to rebalance the system and will operate the valve H] in the proper direction to provide the necessary change in heating of the space under control.

When the humidity responsive device 6i and its associated condenser 6! are used in my control system, the system is responsive to effective tem perature, and the valve l0 may be utilized to con trol the flow of cooling fiuid to the space under control. For correct operation in such a system, the sense of operation of either temperatureresponsive member ID, or valve it) must be reversed from that previously described, so that the Valve will open upon a rise in temperature, and close when the temperature falls. When so connected, the valve I0 is operated in accordance with the resultant of two conditions. temperature and humidity. If it is found desirable to determine the resultant directly rather than reciprocally, the condition-responsive condensers in the input circuit of oscillator 34 may be connected in parallel instead of in series.

It will be seen from the foregoing description,

that my system is very sensitive to changes in the controlling condition, and that a very small force may be utilized by my system to produce a movement of a control device.

While my invention is particularly applicable to temperature and humidity-responsive systems because of these characteristics, it should be apparent to those skilled in the art that my system may be controlled by any condition which is adaptable to vary a reactance, and that it may operate any device which is adaptable to be driven 1 by a suitable motor. For example, the motor of my device might be used to control the position of a recording pen in many commercial recording devices, or to control the governor of a prime mover.

It will also be apparent to those skilled in the art that the rebalancing condenser 63 of my device could be omitted, and the line 85 connected The system would then operate as a two-position control system. That is to say, upon an unbalance of the oscillator outputs in response to a change in the controlling condition, the motor 13 would run to the end of its travel in a direction such as to operate the control means to restore a balance of the controlling condition. The controlling condition would consequently be changed in the opposite sense, and would eventually cause the oscillator outputs to become unbalanced in the opposite sense, and the motor would run to the end of its travel in the opposite direction. The control means would therefore be driven between two extreme positions. Stop means would, of course, be provided to limit the travel of the motor, which might be of the type which is designed to avoid overheating when energized continuously, but prevented from rotating.

While I have described a specific embodiment of my invention it should be understood that the invention is in no sense limited thereto except as set forth in the appended claims.

I claim as my invention:

1. A system for operating a control device, comprising in combination, a source of alternating electrical current of substantially constant frequency, a second source of alternating electrical current, means for varying the frequency of said second source in response to the magnitude of a condition indicative of the need for operation of said control device, means for splitting the output current of one of said sources into two components displaced in phase, a first coupling means for combining one of said components with the output current of the other source so as to pro duce a first beat frequency current, a second coupling means for combining the other of said components with the output current of the other source so as to produce a second beat frequency current displaced in phase from said first beat frequency current, a motor for driving said control device having a two phase winding, and connections between said first and second coupling means and said winding for supplying said motor with two phase beat frequency current.

2. A" system for operating a control device in proportion to the magnitude of departure of a condition from a predetermined value, including in combination, a first source of alternating electrical current of a substantially constant standard frequency, a second source of alternating electrical current normally operating at said standard frequency, means for varying the frequency of said second source in proportion to the magnitude of departure from a predetermined value of a condition indicative of the need for operation of said control device, means for splitting the output current of one of said sources into two components displaced in phase, a first coupling means for combining one of said components with the output current of the other source so as to produce a first beat frequency current, a second coupling means for combining the other of said components with the output current of the other source so as to produce a second beat frequency current displaced in phase from said first beat frequency current, a motor for driving said control device having a two phase winding, connections between said first and second coupling means and said winding for supplying said motor with two phase beat frequency current, and means driven by said motor and associated with said second source for restorin it to its normal operating frequency.

3. A system for operating a control device in proportion to the magnitude of departure of a condition from a predetermined value, including in combination, a first source of alternating electrical current of a substantially constant standard frequency, a second source of alternating electrical current normally operating at said standard frequency, a first reactance means variable in proportion to the magnitude of departure from a predetermined value of a condition indicative of the need for operation of said control device and associated with said second source for regulating the frequency thereof, means for splitting the output current of said one of said sources into two components displaced in phase, a first coupling means for combining one of said components with the output current of the other source so as to produce a first beat frequency current, a second coupling means for combining the other of said components with the output current of the other source so as to produce a second beat frequency current displaced in phase from said first beat frequency current, a motor for driving said control device having a two phase winding, connections between said first and second coupling means and said winding for supplying said motor with two phase beat frequency current, and a second reactance means variable by operation of said motor in a sense opposite to the variation of said first reactance, and associated with said second source for restoring it to its normal operating frequency.

4. A system for operating a control device, comprising in combination, a source of alternating electrical current of substantially constant frequency, a second source of alternating electrical current, means for varying the frequency of said second source in response to the magnitude of a condition indicative of the need for operation of said control device, coupling means for combining the currents from said sources so as to produce a beat frequency current, a motor for driving said control device, a connection between said coupling means and said motor for supplying said motor with said beat frequency current, and a second means for varying the frequency of said second source, said second means being operated by said motor in a sense opposite to said first mentioned means.

5. A system for operating a control device in accordance with the effective temperature of a space, including in combination, a source of alternating electrical current of substantially constant frequency, a second source of alternating electrical current, a first means for varying the frequency of said second source in response to the humidity of said space, a second means for varying the frequency of said second source in response to the temperature of said space, coupling means for combining the currents from said Sources so as to produce a beat frequency current, a motor for driving said control device, a connection betweensaid coupling means and said motor for supplying said motor with said beat frequency current, and a third means for varying the frequency of said second source, said third means being operated by said motor to vary the frequency in a sense opposite to that of the variation produced by said first and second means. 1

6. A system for operating a control device, including in combination, a first source of alternating electrical current of a substantially constant standard frequency, a second source of alternating electrical current normally operating at said standard frequency, means for producing a variation in the frequency of said second source corresponding in magnitude and sense to the variation from a predetermined value of a con dition indicative of the need for operation of said control device, means for splitting the output current of one of said sources into two components displaced in phase, coupling means for combining said components with the output current of said other source so as to produce a two phase beat frequency current corresponding in frequency to the magnitude of said condition variation and in phase relations to the sense of said condition variation, and a connection between said coupling means and said control device for supplying the latter with said heat fiequency current, said control device operating with a speed proportional to said beat frequency and with a direction determined by said phase relations. 1

7. A system for operating a control device, including in combination, a first source of alternating electrical current of a substantially constant standard frequency, a second source of alternating electrical current normally operating at said standardfrequency, means for producing a variation in the frequency of said second source corresponding in magnitude and sense to the variation from a predetermined value of a condition indicative of the need for operation of said control device, means for splitting the output current of one of said sources into two components displaced in phase, coupling means for combining said components with the output current of said other source so as to produce a two phase beat frequency current corresponding in frequency to the magnitude of said condition variation and in phase relations to the sense of said condition variation, a connection between said coupling means and said control device for supplying the'latter with said beat frequency current, said control device operating with a speed proportional to said beatfrequency, and with a direction determined by said phase rela tions, and means operated in unison with said control device and associated with said second source for restoring it to its normal operating frequency.

8. A system for operating a control device, comprising in combination, an electronic oscillator of substantially constant frequency, a second electronic oscillator, impedance means variable in accordance with the magnitude of a condition indicative of the need for operation of said control device and connected to said second oscillator so as to control its frequency, means for splitting the output current of one of said oscillators into two components displaced in phase, a first coupling means for combining one of said components with the output current of the other oscillator so as to produce a first beat frequency current, a second coupling means for combining the other of said components with the output current of the other oscillator so as to produce a second beat frequency current displaced in phase from said first beat frequency current, a motor for driving said control device having a two phase winding, and connections with the frequency and phase relations of the alternating currents supplied to said windings, means responsive to a condition indicative of the need for operation of said control device, variable impedance means operated by said condition responsive means, a source of electrical energy, connections between said source and said motor windings, and means in said connections including said variable impedance means for controlling the frequency and phase relations of the alternating currents supplied to said motor windings in accordance with the magnitude and direction of departure of said condition from a predetermined value.

10. In combination, a control device, an alternating current motor for operating said control device, said motor having two windings displaced in space phase and characteristics of speed and direction of operation variable in accordance with the frequency and phase relations of the alternating currents supplied to said windings, means for supplying alternating electrical currents to said windings, and means responsive to a condition indicative of the need for operation of said control device for controlling the frequency and phase relations of said alternating currents in accordance with the magnitude and direction of departure of said condition from a predetermined value.

duce a first beat frequency current, a second coupling means for combining the other of said components with the output current of the other source so as to produce a second beat frequency current displaced in phase from said first beat frequency current, a motor for driving said control device having a two phase winding, and connections between said first and second coupling means and said winding for supplying said motor with two phase beat frequency current.

12, In combination, a control device, an alternating current motor for operating said control device, said motor having a speed characteristic variable in accordance with the frequency of electrical energy supplied thereto, a source of electrical energy, means for transmitting electrical energy between said source and said motor, means responsive to a condition indicative of the need for operation of said control-device for controlling the frequency of the energy transmitted to said motor in accordance with the magnitude of the variation of said condition from a predetermined value, and means driven by said motor concurrently with said control device for varying the frequency or said energy in a sense opposite to that of said condition responsive means, so as to terminate operation or said motor after said control device has moved an amount dependent upon the magnitude of the variation of said condition.

ALWIN B. NEWTON. 

